Rainbow

[ChadS]

Sorry to bring up an old thread but I'm new to the board and this is one thread to which I felt I could contribute some expert technical expertise.

Please be aware that I am essentially clueless in PS and so what you're doing is a marvel to me. But since you all put the images here for criticism (positive and "constructive") I'm going to provide a very technical analysis of your 'bows.

The first thing to understand is that the center of the rainbow is directly on a line from the sun through your head. If you put the sun directly behind your head the spots your eyes look will be the center of the rainbow arc. From there the primary rainbow will occur at a half-angle of about 42 degrees (84 degrees across). Keep that in mind with the angle of collection for the lens you're using. If the rainbow doesn't subtend the proper fraction of the sky it will look odd to the viewer and they won't necessarily know why.

In William's shot (the bridge) the flat lighting makes it difficult to tell exactly where the sun is but it appears to be up and to the right. Also, for as bright as that rainbow is standing out you'd see the secondary rainbow on the other side of Alexander's dark band about another 9 degrees out (with the colors reversed).

In Denise's shot the rainbow arcs almost all the way across the sky. That would put the sun immediately behind the photographer - but the color of the photo doesn't make it appear at sunrise or sunset at all.

To make a believable rainbow you've got to realize how they form. Our eye tricks us into thinking rainbows form really, really far away because the rays exiting the droplets are almost all parallel for a given color (as if they were at infinity). And it's quite possible to have a rainbow form in clouds that are miles away. However, it's also possible to have a rainbow form from rain drops that are only a few feet from the observer and yet these bows still appear to be somewhere miles away. The takeaway from this is that bows can only form where you can see drops! So in Denise's shot we see a strong rainbow appearing in the parts of the sky that appear crystal-clear blue. And in William's photo the intensity of the 'bow doesn't vary with position in the cloud. Really dark clouds actually create really weak bows - any droplet size distribution of the proper shape to make a cloud go from white to gray certainly is enough to swallow the rainbow light. Often you'll see a bow that "jumps" from one cloud to another. Your mind will fill in that it's connected and it may be if there is a light shower between clouds. But as often as not the rainbow you're looking at is composed of several segments from each cloud you see.

Finally William, the colors at the ends of the rainbow are off. We're used to thinking of purple as being the combination of red and blue. However, in terms of color of light wavelengths "violet" (not purple) is on the short end of visible light whereas red is on the long. If you've ever seen a viloet laser at the limit of visible detection (say 405 or 415 nm) and compared it to a red laser at the extreme long end (from 690 to 720 depending on the set of eyes I'm guessing) there's really nothing remotely close in those two colors. The red extreme of your rainbow is a bit too purplish to be a real rainbow and there's not enough of a well defined blue or aquamarine band.

Again, please don't take my comments as negative. I believe you've got the skills to take these comments and be able to fool someone who really knows much about the physics of rainbows. I'd love to see the result.

[ddt0725]

@Chad - Thank you so much for the very informative input you have provided!! Your critique is very helpful as well as William's directions. As soon as I get a chance, I am going to put all of this together and try to apply another rainbow ...hopefully a more realistic one! Or better yet, maybe someday I will have a camera handy when I see a real one!

Thanks again!
Denise